Plasma enhancement apparatus and method for physical vapor deposition

ABSTRACT

The present invention provides a plasma enhancement method and apparatus for electric arc vapor deposition. The plasma enhancement apparatus is positioned to act upon plasma generated from a plasma source before the plasma reaches a substrate to be coated by the plasma. The plasma enhancement apparatus includes a magnet disposed about a magnet axis and defining a first aperture, and a core member disposed about a core member axis and at least partially nested within the first aperture. The core member defines a second aperture, and the plasma enhancement apparatus is arranged and configured in such a manner that the evaporated cathode source material passes from the cathode source and through the second aperture toward the substrate to be coated by the evaporated cathode source material. The plasma is favorably conditioned as it passes through the plasma enhancement apparatus.

This is a continuation of application Ser. No. 08/092,670, filed Jul.14, 1993, which was abandoned upon the filing hereof, which is acontinuation of application Ser. No. 07/689,313 filed Apr. 22, 1991,which was abandoned upon the filing hereof.

FIELD OF THE INVENTION

This invention relates generally to a vapor deposition apparatus, andmore particularly, to a plasma enhancement apparatus, or "plasma guide,"for physical vapor deposition.

CROSS REFERENCE TO RELATED PATENTS

To the extent that the disclosures of U.S. Pat. No. 3,625,848 to Snaper,U.S. Pat. No. 3,793,179 to Sablev, et al., U.S. Pat. No. 4,448,799 toBergman, et al., and U.S. Pat. No. 4,485,759 to Brandolf are relevant tounderstand the principles of this invention, they are hereinincorporated by reference.

BACKGROUND OF THE INVENTION General

A number of disciplines have been developed over the years in the vapordeposition art for applying or depositing a coating layer on a substratesurface within a vapor deposition chamber. Certain fundamental processsteps are the same for all of the vapor deposition disciplines, althougha large number of variations and techniques in implementing the processsteps have been developed. Generally, the substrate to be coated isplaced within a deposition chamber, which is typically evacuated orpressurized to a desired pressure. The coating material to be depositedon the substrate is generated within or introduced into the chamber, andassumes the form of a plasma that includes gaseous vapors and solidparticulate matter. The plasma may include atoms, molecules, ions, andagglomerates of molecules of the coating material, as well as those ofany desired reactant agents and any undesired impurities. The coating ordeposition process itself occurs by condensation of the plasma coatingparticles onto the substrate surface(s) to be coated.

Vapor deposition coating processes are generally categorized into"chemical" and "physical" vapor deposition disciplines. Both generallyincorporate a deposition or coating chamber in which a "plasma" of thecoating material is produced and projected toward a substrate to becoated. The uses of the coatings applied to substrates, and the shapesand materials of the substrates can vary widely, from decorativecoatings on ceramic or pottery materials, to circuit interconnectionwiring paths on the surfaces of semi-conductor chips, to wear-resistantcoatings on cutting tool and bearing surfaces. Similarly, the physicalnature and properties of the coating materials vary widely, fromconductive coatings, to semiconductive coatings, to those formingelectrical insulators.

Chemical Vapor Deposition

Chemical vapor deposition generally refers to that vapor depositionprocess wherein reactive gaseous elements are introduced into adeposition chamber and react to form gaseous compounds that comprise thecoating plasma. The deposition chamber may be evacuated prior to adeposition "run" to purge the chamber of impurities, but in general,chemical vapor deposition is performed at atmospheric or at positive(above atmospheric) pressure levels. Also typical of chemical vapordeposition techniques is the fact that the plasma particles do notgenerally follow straight-line or line-of-sight paths from the reactivesources to the substrates.

Physical Vapor Deposition

In contrast, physical vapor deposition processes generally requireevacuation of the deposition chamber prior to, and maintenance of anegative pressure level during, the deposition coating process. At leasta portion of the coating material to be deposited is generally presentin the deposition chamber in non-gaseous form. Prior to evacuation ofthe chamber, the typically solid sacrificial source material is actedupon by an energy stimulus that converts the solid source material intoa vaporous plasma of coating material. Once converted into a plasma, acoating source material may be combined with reactive gases or otherelements within the chamber to form coating compounds and moleculesprior to actual deposition thereof onto substrate(s). The coating plasmatypically includes atoms, molecules, ions, ionized molecules, andagglomerates of molecules. The deposition process can be enhanced bycreating ionic attraction between the plasma particles and the substratesurface(s).

There are a number of different physical vapor deposition techniques,which are distinguished by the manner in which the source material isvaporized. The most commonly used physical vapor deposition techniquesfor converting the solid coating source material into a gaseous/vaporplasma are: (a) resistance or induction heating; (2) electron beam orion bombardment; and (3) electric arc.

With resistance and induction heating techniques, the coating sourcematerial is brought to its melting point by an external heat source orby passing high electric current levels through the coating sourcematerial. The source material, or a portion thereof, first melts to amolten liquid state, and then vaporizes to a gaseous state to form thecoating plasma. This technique has been used for depositing thin filmcircuit patterns on hybrid circuit substrates, and for depositingmetalization interconnection patterns and layers on semi-conductor chipsurfaces.

With electron beam and ion bombardment techniques, a molten pool ofcoating source material is created by bombarding the solid coatingsource material with a high-energy beam of electrons and/or ions. Insuch art, the solid source material is typically referred to as a"target", toward which the electrons and/or ions are accelerated. Thebombarding electrons and/or ions impart sufficient kinetic energy to thetarget source coating material, causing atoms, ions, molecules, ionizedmolecules, and agglomerates of molecules to leave the target sourcematerial in the form of a coating plasma. This physical vapor depositionmethod, while more practical than the resistance or inductive heatingmethod for coating larger work pieces such as cutting tools, is costlydue to the expensive equipment required for generating and directing theelectron and/or ion beam toward the target area. The energy level ofcoating plasma particles generated by the two physical vapor depositiontechniques described above is relatively low.

Physical Deposition by Electric Arc

The present invention relates to the third listed physical vapordeposition technique (i.e., to that of electric arc, also referred to ascathodic arc vapor deposition). Various known electric arc vapordeposition techniques are disclosed in U.S. Pat. No. 3,625,848 to Snaperand U.S. Pat. No. 3,793,179 to Sablev, et al. U.S. Pat. No. 4,448,799 toBergman, et al., and U.S. Pat. No. 4,485,759 to Brandolf.

In electric arc physical vapor deposition, an electric arc is struck andmaintained between the coating source material, which is typicallyelectrically biased to serve as a cathode, and an anode that is spacedapart from the cathode. An arc-initiating trigger element is positionedproximate the cathode source and is positively biased with respect tothe cathode. The trigger element is momentarily allowed to engage thesurface of the cathode material, establishing a current flow path thoughthe trigger and cathode. As the trigger element is removed fromengagement with the cathode source, an electrical arc is struck, whicharc is thereafter maintained between the cathode and the anodeelectrodes of the chamber. The electric arc carries high electriccurrent levels, typically ranging from 30 to several hundred amperes,and provides energy for vaporizing the coating source material. The arcterminus is visible on the surface of the cathode, where the arc"touches" the cathode, and is typically referred to as a "cathode spot".One or more of such cathode spots may exist on the cathode surface atone time, depending upon the current present in the arc. The cathodespot(s) randomly move across the surface of the source material,instantaneously vaporizing the coating source material into a coatingplasma. The plasma typically contains atoms, molecules, ions, andagglomerates of molecules, and generally, both ionically charged andneutral particles. Plasma particles created by an electric arc generallyleave the solid source material at significantly higher energy levelsthan those created by the other physical vapor deposition techniques.The electric arc technique has been found to be particularly attractivefor commercial coating applications, particularly to the economicalformation of wear-resistant coatings on surfaces of cutting tools,bearings, gears, and the like.

One type of coating source material that is often used for the cathodeof electric arc vapor deposition machines is titanium (Ti). When atitanium source material is used, a reactive gas such as nitrogen (N) isoften introduced into the deposition chamber during the vaporization ofthe titanium source. The nitrogen gas reacts with the titanium, and thecoating plasma within the chamber comprises Ti, N₂ and TiN. TiN forms agold-colored coating that has been found to be a very durable coatingfor cutting tools and the like.

Another desirable cathode material is graphite, which produces carbon(C) plasma that forms a diamond-like coating when deposited. Chemicalvapor deposition techniques are available for forming such diamond-likecoatings, but the amount of hydrogen (H) present in the system must becarefully controlled in order to eliminate or minimize the formation ofundesirable hydrocarbons in the structure of the coating film. By usingelectric arc vapor deposition, the system could be evacuated and madesubstantially hydrogen-free, and then a controlled partial pressure ofhydrogen could be injected into the system. However, it is relativelydifficult to form homogeneous, smooth carbon coatings by electric arcphysical vapor deposition techniques, because the arc tends to remain infixed spots on a graphite cathode, dislodging undesirable, large pieces(macroparticles) of the graphite cathode into the coating plasma.

In all deposition coating processes, it is desirable to form smooth,homogeneous films on the substrate which are free of macroparticles,which can otherwise degrade film properties. Attaining this goal withelectric arc deposition is more difficult than with other types ofphysical vapor deposition, since it is difficult to control the highenergy levels incident to use of an arc, and since the presence of thearc energy within the deposition chamber has oftentimes eliminated useof or minimized the effectiveness of apparatus and techniques availableto other physical vapor deposition methods. Attempts have been made to"shield" the macroparticles, but any such shielding is relativelyinefficient because a portion of the coating material is lost to theshield, and further, the shield must be periodically replaced as coatingmaterial accumulates on it.

Those skilled in the art are aware of the need to control movement ofthe arc or cathode spot(s) over the surface of the cathode source so asto maximize the efficiency of the cathode disintegration and theuniformity of the plasma generated from the source. It has beenrecognized in the art that magnetic and electric fields can be used tohelp maintain the cathode spot(s) on the desired evaporation surface(s)of the cathodic source, and to control the movement pattern of thecathode spot(s) over the evaporation surface. It has also beenrecognized in the physical vapor deposition art that electric andmagnetic fields can be used to some advantage in helping (1) to directthe coating plasma, and particularly an ionized plasma, toward thesubstrate to be coated; (2) to produce higher levels of vaporionization; and (3) to increase the deposition rate. However, none ofthe prior art structures or methods has provided a single simple,efficient, and practical approach for using magnetic and electricalfields in a manner that simultaneously provides all of these features inan electric arc physical deposition environment. Further, none of theprior art attempts at solving such problems has provided the flexibilityto be readily applied to different cathode source materials requiringdifferent deposition conditions, such as titanium and carbon. Thepresent invention provides a simple yet effective way of simultaneouslyaddressing the above-described needs/problems and concerns of theelectric arc physical vapor deposition art.

SUMMARY OF THE INVENTION

The present invention provides a plasma enhancement method and apparatusfor electric arc vapor deposition. The plasma enhancement apparatus ispositioned to act upon plasma generated from a plasma source before theplasma reaches a substrate to be coated by the plasma. The plasmaenhancement apparatus includes a magnet disposed about a magnet axis anddefining a first aperture, and a core member disposed about a coremember axis and at least partially nested within the first aperture. Thecore member defines a second aperture, and the plasma enhancementapparatus is arranged and configured in such a manner that theevaporated cathode source material passes from the cathode source andthrough the second aperture toward the substrate to be coated by theevaporated cathode source material. The plasma is favorably conditionedas it passes through the plasma enhancement apparatus.

The present invention combines the use of electric and magnetic fieldsgenerated by plasma enhancement apparatus within and/or around thedeposition chamber to directly control and influence the creation andflow of the coating plasma from the source cathode to the substrate. Theprinciples of this invention provide for (1) increased ion density atthe cathode, yielding increased thermionic emission; (2) stabilizationof the arc on the cathode surface at relatively low arc currents; (3)the facilitation of evaporation of heretofore difficult materials suchas carbon, refractory metals, and doped ceramics; and (4) the reductionof macroparticle emission from the cathode. Further, the presentinvention provides a method of coating by electric arc vapor depositiona substrate with a diamond-like film that is virtually free of hydrogen.

This invention provides for creation of a controllable plasmaconvergence zone intermediate the source and substrate which purifiesthe plasma stream of macroparticles and increases ionization energy inthe plasma stream, yielding coating films of increased density,hardness, and better adhesion and enhancing synthesis reactions duringreactive deposition. The present invention also enables greaterflexibility in control over the shape and direction of the plasma streamwhich can be made to correspond more closely to the desired depositionprofile for the substrate.

BRIEF DESCRIPTION OF THE DRAWING

Referring to the Figures, wherein like numerals represent like partsthroughout the several views:

FIG. 1 is a diagrammatic view of an electric arc deposition chamber,including a plasma enhancement apparatus configured according to apreferred embodiment of the present invention;

FIG. 2 is an enlarged sectional view illustrating a first embodiment ofthe plasma enhancement apparatus of FIG. 1 together with the immediatelyadjacent deposition chamber structure;

FIG. 2a is a digrammatic view of the magnetic fields generated by acurrent passing through the magnet coil of the plasma enhancementapparatus of FIG. 2;

FIG. 3 is a sectional view illustrating a second embodiment of theplasma enhancement apparatus of FIG. 1 together with the immediatelyadjacent deposition chamber structure;

FIG. 3a is a digrammatic view of the magnetic fields generated by acurrent passing through the magnet coil of the plasma enhancementapparatus of FIG. 3;

FIG. 4 is an experimental results graph of substrate current as afunction of voltage across the substrate for a variety of Gauss settingsfor the plasma enhancement apparatus shown in FIG. 2;

FIG. 5a is an experimental results graph of intensity for the variousnitrogen and titanium atoms and ions present in the deposition chamberas a function of magnetic field strength generated by use of the plasmaenhancement apparatus shown in FIG. 2;

FIG. 5b is an experimental results graph of intensity for the variousnitrogen and titanium atoms and ions present in the deposition chamberemploying the plasma enhancement apparatus shown in FIG. 2, as afunction of pressure within the deposition chamber;

FIG. 6 is an experimental results graph of surface roughness of a vapordeposited substrate film coating as a function of magnetic fieldstrength generated by use of the plasma enhancement apparatus shown inFIG. 2;

FIG. 7 is an experimental results graph of substrate current as afunction of voltage across the substrate for magnetic fields of 0 and500 Gauss generated by use of the plasma enhancement apparatus shown inFIG. 3;

FIG. 8 is an experimental results graph of substrate current as afunction of magnetic field strength generated by use of the plasmaenhancement apparatus shown in FIG. 3 for environments of hydrogen andargon; and

FIG. 9 is a top elevational view of the arc enhancement apparatus shownin FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Vapor Deposition System

Referring to the drawing, there is generally illustrated in FIG. 1, adiagrammatic representation of an electric arc vapor deposition systemwith which the present invention can be used. It is emphasized that FIG.1 is only a diagrammatic representation of such a system, whichgenerally schematically illustrates those basic portions of an electricarc vacuum vapor deposition system that are relevant to a discussion ofthe present invention, and that such diagram is by no means complete indetail. For a more detailed description of electric arc vapor depositionsystems and various portions thereof, one may refer to U.S. Pat. Nos.3,793,179 to Sablev, et al., 4,485,759 to Brandolf, 4,448,799 toBergman, et al., and 3,625,848 to Snaper. To the extent that suchadditional disclosure is necessary for an understanding of thisinvention, the disclosures and teachings of such patents are hereinincorporated by reference.

Referring to FIG. 1, there is generally illustrated at 10 a vapor vacuumdeposition chamber having a first wall chamber portion 10a and a secondwall chamber portion 10b appropriately connected together (by means notillustrated) to form an enclosed inner cavity 11 that defines adeposition chamber in which substrates are to be coated. A vacuumpumping system, diagrammatically illustrated at 12, communicates withthe inner cavity 11 by means of an outlet port 11a, and is operable tosuitably evacuate the chamber, as is well known by those skilled in thepart. Appropriate means for inserting reactive or inert gases to theinner cavity 11 during various process steps of the depositionprocedures are generally illustrated at 13 and communicate with theinner cavity 11 by means of an inlet port 11b. Other general purposeinlet and outlet ports may be provided for opening into the inner cavity11, but are not illustrated or described herein.

A source of coating material 15, referred to in FIG. 1 as the "Cathode,"represents the origin of coating vapor or "plasma" for the vapordeposition coating process, and represents one electrode of an arcgenerating apparatus. In an electric arc vapor deposition system, suchsource of coating material generally represents a physical mass ofcoating material, such as titanium, in solid form. The physical shape ofthe source material can vary, for example, from cylindrical, torectangular to irregular. The type of source material can alsosignificantly vary, from conductive, to semiconductive, to insulative.In a preferred embodiment of the invention, the source material istitanium. The titanium source 15 is mounted in the deposition cavity 11by appropriate mounting means, generally illustrated at 16 in FIG. 1,and typically has at least a portion thereof projecting outwardlythrough one of the chamber walls to the atmospheric environment. In thediagrammatic illustration of FIG. 1, the mounting means 16 isillustrated as projecting through the second chamber wall portion 10b.Due to the high electrical current levels passing through the cathodeduring electric arc vapor deposition processes, the cathode getsextremely hot, typically requiring external cooling. Such cooling istypically provided by a water flow-through system, schematicallyillustrated at 17 in FIG. 1, which communicates with the cathodemounting apparatus 16 by means of a flow path 18. Appropriate vacuumseal and electrical isolation means, generally illustrated at 19, areprovided for maintaining the vacuum within the deposition cavity 11 andfor electrically isolating the cathode source 15 from the depositionchamber wall portions 10a and 10b.

A primary DC power supply, designated as "cathode power" in FIG. 1, forgenerating and maintaining the electric arc energy of the system isillustrated at 20. The negative terminal of the power supply 20 iselectrically connected to the cathode 15 through the cathode mountingmeans 16 by means of a signal flow path 21. The positive terminal of thepower supply 20 is directly connected to the wall chamber portion 10a bymeans of a signal flow path 22.

Those items to be coated within the chamber 11 are typically referred toas substrates, and are generally illustrated at 26 in FIG. 1. Thesubstrates are appropriately mounted within the chamber, and may also beelectrically biased, as diagrammatically illustrated by the substratebias supply functional block 27 and the signal flow path 28. Thesubstrates 26 can also be heated by appropriate heating means (notillustrated). It will be understood that the relative spacingsillustrated between components such as the cathode, anode andsubstrate(s) in FIG. 1 are diagrammatic in nature and are not intendedto be represented to scale or as they would actually appear relative toone another in an operative system.

An arc-initiating trigger assembly is diagrammatically illustrated at30. The trigger assembly 30 may be of any appropriate construction, suchas for example the pneumatically operated trigger apparatus of U.S. Pat.No. 4,448,799, or of any other configuration that is operable toinitiate an arc between the cathode 15 and the wall chamber portion 10a.Electrical power for initiating an arc on the cathode surface 15a isprovided to the trigger from the output terminal of the power supply 20,typically through a resistor 32 and a signal flow path 33. The signalflow path 33 passes through the chamber wall 10b by means of aninsulating seal member generally designated at 34. When anarc-initiating wire member is positioned so as to engage the uppersurface 15a of the cathode 15, an electrical closed circuit isestablished from the positive output terminal of the power supply 20,through the resistor 32, the signal flow path 33, the arc-initiatingtrigger wire 30a, through the cathode 15 and cathode support structure16 and back to the negative output terminal of the power supply 20. Whenthe trigger 30 operates so as to lift the wire member out of engagementwith the upper surface 15a of the cathode source 15, the electricalcircuit path between the wire and cathode surface 15a is broken, causingan electrical arc to jump the gap therebetween and to initiate anelectric arc on the cathode surface 15a. In an evacuated chamber 11,upon initiation of the electric arc, the arc path immediately extendsbetween the cathode source 15 and the anode portions of the chamber, andis thereafter maintained by the power supply 20. It will be understoodthat a number of variations of applying and supplying electrical currentto trigger assemblies such as 30 can be configured, as will beappreciated by those skilled in the art, and that the particulardiagrammatic representation illustrated in FIG. 1 is only conceptual innature.

As previously described herein, such electric arc paths carry highelectric current levels, typically in excess of 30 amperes. The highconcentration of electric energy passing through the arc(s), visible asintensely bright spots on the cathode surface 15a, liberates cathodematerial to form a coating vapor or plasma, generally illustrated at 40in FIG. 1. Material liberated from the cathode surface generally travelsoutwardly from the cathode source surface 15a. The substrate 26 isappropriately mounted and/or biased so as to intercept the coating vapor40, and the substrate 26 is coated thereby, in manners well-known in theart.

Plasma Enhancement Apparatus

The present invention provides a plasma enhancement apparatus 50 (alsogenerally referred to herein as a "plasma guide") positioned in thecavity 11 between the titanium cathode 15 and the substrate(s) 26. Thoseskilled in the art will recognize that the plasma enhancement apparatus50 need not be placed entirely within the cavity 11, so long as theplasma guide 50 is positioned to act upon the plasma leaving thecathode. In this regard, the plasma enhancement apparatus itself mayfunction as a part of the cavity enclosure.

Referring to FIG. 2, a preferred embodiment of the plasma enhancementapparatus 50 includes a magnet coil 51 and a cooling jacket 52, whichare enclosed in a steel casing 53. The magnet coil 51 is operativelyconnected to a power supply designated generally as "magnet power" at 57by means of signal flow paths 58a and 58b through insulated ports 59aand 59b, respectively. When the magnet power 57 is activated, currentflows through the magnet coil 51 and generates electric and magneticfields, as will be discussed further below.

The cooling jacket 52 is preferably included, but the invention is notdependent thereon and should not be limited thereby. Where the coolingjacket 52 is provided, it is operatively connected to appropriatecooling means 57 via a coolant flow path 58, which passes through aninsulated port 59 in the chamber wall 10a, as shown in FIG. 1. As withthe cathode, the cooling medium for the plasma enhancement apparatus ispreferrably water.

In a preferred embodiment, the casing 53 and its contents, namely, themagnet coil 51 and the cooling jacket 52, generally take the shape of acylindrical shell aligned generally coaxially with the cathode axis, andhaving an coil inner radius R₂ as shown in FIG. 9, as well as FIG. 2.However, it cannot be overemphasized that the present invention is notlimited by any particular shape of the plasma enhancement apparatus, andthat any number of configurations may be used.

The plasma guide 50 further includes a core member 60, which has a coreouter radius R2 and nests within the coil inner radius R₂ of the casing53. The core member 60 defines an aperture 64 having a radius of 25.4mm, through which the majority of the plasma 40 travels. The core membermay be constructed from a variety of materials, magnetic andnon-magnetic, depending on the application. The axial thickness of theplasma guide 50 is preferably 75.0 mm. Again, those skilled in the artwill recognize that the invention is not limited to round cores or coresdefining round apertures, but that various configurations will work andmay be desirable for particular applications.

According to a preferred embodiment, the core member 60 includes a firstcylindrical shell 61, having an approximate axial thickness of 35 mm,and a second cylindrical shell 62, having an approximate thickness of 5mm. The first and second cylindrical shells 61 and 62 are separated byceramic spacers (not shown) to cooperatively define a cylindrical shellvoid 63, having an approximate axial thickness of 25 mm, therebetween.In this particular embodiment, the core 60, comprising the shells 61 and62 and the spacers (not shown), are secured relative to the magnet coil51 by friction fit. Those skilled in the art will recognize that othermeans are available to accomplish this task, and that the coil innerradius can be larger than the core outer radius.

Those skilled in the art will recognize that the present invention wouldalso function with a permanent magnet in place of the electromagnet 51.In fact, a permanent magnet may be desirable once an optimal fieldstrength has been determined because the use of a permanent magneteliminates a parameter from the process that would otherwise requirecontrol. Moreover, a permanent magnet configured in the shape of thecore could be substituted in place of the electromagnet and the core.

Currents of up to 70 Amps through the magnet coil produced a maximumfield strength of 1500 Gauss measured along the magnet coil axis. Theresulting magnetic fields are shown in FIG. 2a, and the net emittedplasma stream 40 is shown in FIG. 2. The plasma 40 tends to converge ina "focus zone" 44, which is bordered by the void 63 and extends adistance along the axis 48 of the plasma enhancement apparatus 50. Theeffects of this convergence or focusing of the plasma stream 40 areexplained in greater detail below.

Experimental Results for First Core and Titanium Cathode

Using a titanium cathode in a nitrogen atmosphere, an apparatusconfigured according to the preferred embodiment described above (andillustrated in FIG. 2) was operated within a Langmuir probe experimentalsystem. The substrate was coaxially positioned relative to the face ofthe titanium cathode, and at a distance of 375 mm. The substrate, whichwas 12.7 mm in diameter, was recessed into a ceramic fixture. A groundedshield 1.2 mm thick with an aperture of 11.87 mm was placed 1.0 mm infront of the substrate.

Plasma emission was monitored through an observation tube aimed tointersect the symmetry axis 375 mm in front of the cathode. Light fromthe emission was transmitted through a quartz window, through a quartzfiber optic cable to the input slit of a 0.5 m Ebert-type Jarrel-Ashscanning monochrometer. The monochrometer was sensitive in the range230-990 nm with a resolution of less than 0.1 nm, and the acceptanceangle was 4°. Deposition rates on the substrate were determined using amicrobalance with a repeatability of 20 mg. The average surfaceroughness was measured with a Dektak profilometer.

The current was initially set to create a magnetic field strength of 890Gauss, the nitrogen pressure at 20 mTorr, the cathode current at 40amperes, and the substrate bias at -80 volts. For the conventional arcexperiments the plasma guide was removed and the cathode to substratedistance was 300 mm (the difference being the length of the plasma guide50).

Substrate current was measured as a function of applied voltage acrossthe substrate, and as a function of magnetic field strength, and theresults are shown in FIG. 4. A voltage-current curve for theconventional arc under similar conditions is also shown for reference.In FIG. 4, positive ions collected by a negative voltage are shown as apositive current and electrons collected by a positive voltage are shownas a negative current. It can be seen that the positive ion currentsaturates at negative voltage. The saturated ion current increases withincreasing magnetic field strength at a rate that is nearly linear untila magnetic field strength of approximately 890 Gauss. Above 890 Gauss,the saturated ion current stays approximately the same. Those skilled inthe art will recognize that the experimental results shown in FIG. 4indicate that use of the plasma enhancement apparatus generates moreplasma and at higher energy levels, as discussed further below.

The saturated current collected at a negative bias is primarily due tothe flux of titanium and nitrogen ions entering the sheath separatingthe plasma from the substrate. The application of a magnetic field in aplasma optics system can have a significant effect on ion flux levels,as has been previously shown in the art. The increase in ion flux is aresult of plasma focusing and the creation of additional ions throughelectron impact ionization. The motion and density of electrons in themagnetic field greatly increases the probability of electron particlecollisions. As recognized by those skilled in the art, the probabilityof electron molecule inelastic collisions is proportional to the squareof the magnetic field strength. If these collisions are energeticenough, excitation, dissociation of molecular species, and ionizationcan occur.

Electron energy was estimated from the positive current in the negativepotential region before ion saturation using a method known in the art,and the electron temperatures are listed below in Table A.

                  TABLE A                                                         ______________________________________                                        Magnetic Field                                                                          kTe         n           -Vf                                         (Gauss)   (eV)        (× 10.sup.10 cm.sup.-3)                                                             (V)                                         ______________________________________                                         0         2.5 ± 1.5           1.0 ± 0.4                                335        6.0 ± 1.5                                                                              .80 ± .15                                                                             5.8 ± 0.4                                670       10.0 ± 1.5                                                                             1.01 ± .26                                                                             8.9 ± 0.4                                890       12.0 ± 1.5                                                                             1.48 ± .32                                                                             5.5 ± 0.4                                1450      25.0 ± 2.0                                                                             1.66 ± .32                                                                             2.5 ± 0.4                                ______________________________________                                    

The results show the electron temperature increasing nearly linearlywith magnetic field strength to a maximum of 25 eV at 1450 Gauss. Listedbelow in Table B are the ionization and dissociation threshold energiesfor the plasma species present in this experiment.

                  TABLE B                                                         ______________________________________                                        Species                                                                       ______________________________________                                                   Ionization Threshold (eV)                                          N2+        15.6                                                               Ti+        6.8                                                                N+         14.6                                                                          Dissociation Energy (eV)                                           N          9.9                                                                ______________________________________                                    

These results indicate that electrons at higher magnetic field strengthsare more than energetic enough to dissociate and ionize other species.The electron temperatures calculated here are for electrons in thevicinity of the substrate traveling perpendicular to the substrate.Electrons in the plasma guide closer to the cathode probably have muchhigher temperatures. This is indicated by the intensity of the plasmaemission coming from this area.

Table A also lists the plasma density n, and the floating potential vfas a function of magnetic field strength. The plasma density wascalculated from the electron temperature kTe, the saturated ion current,and the average charge per ion. The floating potential was measureddirectly, and the plasma potential can be roughly estimated from thesaturation point of the negative current curves, as will be recognizedby those skilled in the art.

Emission spectrometry was used to detect and identify species present inthe plasma over the wavelength range 230-900 nm. The intensity of lightof a particular wavelength is a reliable indicator of the presence andintensity of a particular atom or ion. Plasma emission was monitored atthe same distance as the Langmuir probe, with the Langmuir proberemoved. Measurements were made as a function of magnetic field strengthand nitrogen pressure. The results, which are presented graphically inFIGS. 5a and 5b, show the presence of ionized and excited titanium andsignificant amounts of ionized and excited molecular and atomicnitrogen. This is in contrast to the conventional arc process wheremolecular nitrogen emission intensity is relatively weak and atomicnitrogen emission is not present at all.

Emission from decaying Ti, Ti+, N₂, N₂ +, N, and N+ species wasobserved. Emission from Ti² + and N² + lines were not identified. FIG.5a shows the variation in emission intensity with magnetic fieldstrength for the strongest Ti, Ti+, N₂, N₂ +, N and N+ lines. All linesare strongly influenced by magnetic field strength. In FIG. 5a, it canbe seen that there is an especially strong association between theintensity of emission of nitrogen species and magnetic field strength.The presence of N₂, N₂ +, N and N+ emissions which increase nearlylinearly with magnetic field strength indicates that electron impactexcitation, dissociation, and ionization of nitrogen is occurring. Theexcitation thresholds for these emissions are 11.1, 18.7, 12.0 and 20.7eV respectively. Electron temperature estimates made from the Langmuirprobe experiments show that electron temperatures exceeding theseexcitation thresholds are reached.

All nitrogen emissions including N₂ +, N₂, N+ and N peak in the magneticfield strength range of 900 to 1200 Gauss. The rapid decline in N₂emission intensity and saturation of N₂ + emission intensity may be theresult of nearly complete dissociation and ionization of N₂. Theseemission features also correlate with the behavior of the ion andelectron saturation currents described in the Langmuir probe experimentsat the same conditions. The saturation currents increase linearly withincreasing magnetic field strength and then peak in the same magneticfield strength range of 900 to 1200 Gauss.

The Ti+, and Ti emission lines as shown in FIG. 5a, increase rapidly upto 335 Gauss, above which the emissions level off. From 0 to 335 Gauss,the steep, nearly linear increase in the titanium emissions is probablydue to plasma focusing and electron impact ionization. The abruptsaturation of the titanium emission lines at 335 Gauss correlates to anelectron temperature of approximately 6 eV (based on previously reportedresults) which is close to the ionization threshold of titanium. Theabrupt saturation of the titanium emission lines may be the result ofnearly complete ionization of titanium. The presence of the excitedtitanium emission line which imitates the behavior of the ionizedtitanium emission line at a lower intensity is probably due to threebody electron recombination as described below.

FIG. 5b shows the variation in emission intensity with nitrogen pressureat a constant magnetic field strength of 890 Gauss for the same emissionlines as in FIG. 5a. The characteristic features of this graph aresimilar to those done with the conventional arc (0 magnetic fieldstrength). The most notable difference is the high intensity of thenitrogen emission lines. Between 0 and 15 mTorr, the increases in thenitrogen and titanium emission may be attributable to charge exchangereactions of the type Tn^(n+) +N₂ →Ti.sup.(n-1)+ +N₂ +.

It is believed that the rapid decrease in the intensity of the N₂ +emission above 15 mTorr occurs because the initially high energy ofTi² + species is lost in collisions with nitrogen and falls below the14.0 eV threshold energy needed for this reaction to occur. The Ti+ toTi reaction does not occur because it requires an excessively high ionthreshold energy of 32.3 eV.

In the region above 15 mTorr, the behavior of the Ti+ and Ti emissioncan be attributed to the three body reaction Ti^(n+) +e=N₂→Ti.sup.(n-1)+ +N₂. The probability of this reaction increases withincreasing nitrogen concentration. This is shown in FIG. 5b by thedecline of the Ti+ emission accompanied by a rise in the Ti emission andthe decline of both species above 40 mTorr.

These results and observations indicate that in the magnetic field ofthe enhanced arc apparatus, electronparticle collisions result insignificant excitation, dissociation, and ionization of titanium andnitrogen species. In addition to the inelastic electron-particlecollisions, charge exchange and three body reactions typical of theconventional arc are still occurring. Based on the results from theLangmuir probe and the emission spectrometry and the logicalinterpretations thereof, it appears that the number density of nitrogenions to titanium ions and the resulting contribution of nitrogen ions tothe ion flux on a substrate is significant. This is in contrast to theconventional arc process where nitrogen ions contribute a very smallamount to the current on a substrate.

Finally, a direct comparison of the emission intensity of the N₂ +, N₂,Ti+, and Ti lines studied here showed that emissions in the conventionalarc system were only 2.3, 1.3, 25 and 11 percent respectively, of theemissions in the enhanced arc system under the same operatingconditions. This supports the conclusion that significant enhancement oftitanium and nitrogen excitation and ionization is occurring in theenhanced arc system.

The vapor being deposited on the substrate was found to be 100 percentionized using a recognized ion exclusion method. The ionized fraction ofthe vapor impinging on the substrate was determined by comparing thedeposition rate while excluding ions, to the deposition rate when iondeposition was allowed. Although the graphs of FIGS. 5a and 5b indicatethat some amount of nitrogen and titanium atoms are present during thedeposition process, it is believed that this is not the case at eitherthe convergence zone or the substrate. Rather, it appears that somelimited "recombination" of particles occurs in transit between theconvergence zone of the plasma stream and the substrate.

Ion deposition was done at a magnetic field strength of 890 Gauss for 30minutes. Ion exclusion deposition was done at the same parameters,except a screen with a transparency of 0.903 was placed 1 cm in front ofthe substrate and biased at -100 V to collect ions. A Debye sheathsurrounding the wires enhances the effective ion stopping power of thescreen. The substrate was also biased at +30 V to repel any ions thatmade it through the screen.

The result was no gain in mass when ions were excluded from deposition.No measurable amount of neutral macroparticle flux was included in filmdeposition. Ionization percentages of 68 to 83 percent in theconventional arc process reflect primarily the deposition ofmacroparticles. No mass gain under ion exclusion deposition conditionssupports the conclusion that 100 percent of the vapor is ionized in theenhanced arc process.

The average charge per ion was found to be 2.08±.28e. The average chargeper ion was determined from the deposition rate and the collected ioncharge on a substrate. The deposition rate was measured in mass gainedper second per area on a substrate clamped in a fixture exposing adeposition area of 3.23 cm². Due to gas scattering, the area increasedto approximately 3.53 cm² at 20 mTorr.

The collected ion charge was determined using a value of ion currentdensity obtained from the Langmuir probe system for the same parametersused in deposition. The substrate temperature was less than 220° C.throughout deposition. The atomic ratio of nitrogen to titanium in thefilm was determined using XPS.

The average charge per ion was determined assuming that the nitrogenmass contribution to the film was from ionized molecular nitrogen.(i.e., the ion flux producing the film includes nitrogen ions as well astitanium ions.) This is in contrast to the conventional arc processwhere the average charge per ion determined assuming the nitrogen ioncontribution is negligible. In the present experiment, if the nitrogenion contribution is discounted, the calculated average charge per ionincreases by almost 300 percent. The nitrogen flux is also assumed tocome from ionized molecular nitrogen. If the ionized nitrogen flux iscomposed of 10 percent ionized atomic nitrogen (a reasonable estimateconsidering emission spectrometry results) the average charge per ionwould be reduced to 1.79e.

The average charge per arriving atom is also a product of the stickingcoefficient of the ions to the substrate. A sticking coefficient of0.9±0.1 was used, which is for low energy metal atoms impinging surfacesto which they have a high affinity. An acceleration of the ions and thepresence of impinging nitrogen ions in the enhanced arc system may lowerthe sticking coefficient somewhat. The error in the average charge perion primarily reflects uncertainties in the sticking coefficient and inthe stoichiometry.

Using conventional arc deposition techniques at 20 mTorr, the averagecharge per ion is approximately 1.6e. The 2.08e achieved with thepresent invention reflects higher ionization levels and percentages inthe enhanced arc system. This value was also found at nearly twice thedistance and half the cathode current used in determining theconventional arc data. At similar parameters the average charge per ioncalculated here probably would increase further.

FIG. 6 shows the variation in surface roughness of the coating depositedon the substrate as a function of magnetic field strength. The zeromagnetic field strength value was obtained with the conventional arcsystem (i.e., no plasma enhancement apparatus). High speed steelsubstrates (polished to approximately 150 Angstrom finish) were placed225 mm in front of the cathope, and films were deposited for 15 minutes.The average surface roughness was measured before and after filmdeposition and the difference plotted in FIG. 6.

It can be seen in FIG. 6 that the average surface roughness decreasesrapidly down to a minimum of 80 Angstroms at 1450 Gauss magnetic fieldstrength. SEM analysis of the surface for the film deposited at 1450Gauss showed nearly no macroparticles. Similarly, the film deposited at890 Gauss also showed very few macroparticles. The small increases inaverage surface roughness of the samples deposited at 890 and 1450Gauss, which can be seen as small ripples on a micrograph, are dueprimarily to etching from ion bombardment, which is indicative of theHall acceleration of the ions in the magnetic field.

The reduction and elimination of macroparticles in the enhanced arcsystem can be attributed to one or more of four effects. One effect isdue to geometry and has been previously recognized by those skilled inthe art. Macroparticles leaving the cathode in the enhanced arc systemat less than 55° from the cathode surface will collide with the plasmaguide, and a large percentage of the macroparticles typically leave thecathode at angles of less than 30°. While such "shielding" ofmacroparticles is inherent in the structure of the present invention,the effectiveness of the present invention is attributed primarily tothe elimination of macroparticles by focusing the plasma stream; thedifference being that the present invention, in effect, "recycles" themacroparticles.

A second effect is due to the modification of the arc discharge in themagnetic field enhanced by the present invention. The plasma enhancementapparatus creates magnetic fields that facilitate rapid movement of thearc across the cathode surface, resulting in a distinct reduction in theamount of melted area around the arc craters on the cathode, which aretypically a source of macroparticles. Splitting of the arc into multiplecathode spots also occurs in the enhanced magnetic field, resulting inlower current densities and less melting of the cathode surface. SEManalysis of the surface of the cathode used in the enhanced arc systemshowed a distinct reduction in the amount of melted area and smallercrater sizes on average in relation to a cathode used in theconventional arc system.

A third effect is a result of cathode "poisoning," as fewer and smallermacroparticles are produced from a cathode having a nitride surface. Theproduction and confinement of large numbers of nitrogen ions in thevicinity of the cathode in the enhanced arc system contributes to thenitriding of the cathode surface. This is shown by an increase in theyellowing of the cathode after having been used in the enhanced arcsystem as compared to a cathode subjected to conventional arctechniques.

A fourth effect is a result of the evaporation of macroparticles bycollisions with electrons. The dense energetic electron conditions inthe convergence zone generated by the plasma enhancement apparatus are alikely explanation for the large reduction in macroparticles withincreasing magnetic field strength.

The enhanced plasma optics system of the prevent invention increases theionization and energy of the flux impinging TiN films during deposition.Inelastic collisions with energetic electrons in the strong confinedmagnetic field of the apparatus results in an increase in the excitedand ionized species density. Dissociation and ionization of nitrogen andthe resulting contribution of nitrogen ions to the plasma flux isespecially apparent. The average charge per ion at the substrate isincreased over the conventional arc case to approximately 2.1e. Theionized fraction of the vapor is also increased to 100 percent in theconvergence zone and proximate the substrate; the neutral vapor andmacroparticle contribution to mass gained at the substrate was measuredto be zero. Accordingly, deposited films are nearly free ofmacroparticles.

Alternative Plasma Enhancement Apparatus

FIG. 3 shows an alternative embodiment of a plasma guide 50' accordingto the principles of the present invention. The plasma enhancementapparatus 50' of FIG. 3 is similar in detail to that of FIG. 2 with thesubstitution of core 80 for core 60 which is symmetrically disposedabout the axis 48' of the plasma enhancement apparatus 50'. The magnetcoil 51' has an outer coil radius R3' of 45 mm and an axial thickness of100 mm. Core 80 includes a plurality of cylindrical shells 81a-81e, eachhaving an approximate axial thickness of 5.0 mm. Each of the cylindricalshells 81a-81e rests on a ceramic spacer (not shown) to definecylindrical shell voids 82a-82e, each having an approximate axialthickness of 12.0 mm. In this particular embodiment, the core 80,comprising the shells 81a-81e and the spacers (not shown), are securedby bolts (not shown) to the magnet coil 51.

A current through the magnet coil 51 generates the magnetic fields shownin FIG. 3a, and the net emitted plasma stream 40' is shown in FIG. 3.The operative effect of the core 80 is to create a magnetic field with a"longer" axial focus zone 44', through which the plasma stream 40'passes. The "path lines" 40a' and 40b', defining the general path of theplasma 40, represent the "effective magnetic field" generated by thecore 80.

In addition to enhancing the evaporation, transportation, and depositionof the plasma, the present invention facilitates the selection andsubstitution of varied core configurations in order to create magneticfields of varied magnitude, shape, and axial focal length, accomodatingvarious deposition applications and the use of widely differing sourcematerials. Just as the first core 60 is deemed suitable for use inconjunction with the titanium cathode 15, the second core 80 is deemedwell suited for use in conjunction with a graphite cathode 75, asexplained below. In fact, use of the second core 80 in the manner setforth below produces diamond-like coating films that are virtually freeof hydrocarbons.

Experimental Results for Second Core and Graphite Cathode

Using a graphite cathode in a controlled partial pressure hydrogenatmosphere, experiments were conducted with an apparatus configuredaccording to the preferred embodiment described above (and illustratedin FIG. 3). The high purity graphite cathode had the followingcharacteristics:

Grade: Poco SFG-2

Density: 1.8 gms/cm³

Pore Size: 0.2 um

Particle Size: 1 um

Purity: 5 ppm.

The cathode 75 was arranged coaxially in relation to the magnet coil 51,which is 90 mm in diameter and 100 mm thick (measured axially). The DCcurrent supplied to the magnet coil 51 was controlled for producing anaxial magnetic field with a strength varying in magnitude from 0 to 1000Gauss. The shape and the fringing effect of the lines of force can beoptimized by the magnetic core pieces 81a-81e positioned inside theplasma enhancement apparatus 50'. The working vacuum during arcevaporation was around 10-6 Torr. Hydrogen and argon gases were meteredby conventional Tylan mass flow controllers, the pressure measurementwas performed by means of a MKS baratron transducer, and the substratetemperature was determined using an infrared optical pyrometer.

The experiments were conducted with substrates made of polished highspeed steel, WC, and silicon. After having been thoroughly degreased inorganic cleaning the samples were pressed onto a water cooled stainlesssteel substrate holder. Before the coating phase, the substrate(s) weresubjected to an additional cleaning by igniting a Hydrogen/Argon glowdischarge at reduced partial pressure of about 10 to 100 mTorr at a biasvoltage of -1000 V for 10 minutes. This plasma etching phase was foundto be important for conditioning the substrate surface prior todeposition and for improving the adhesion of the carbon layers. It isbelieved that the preparatory high energy bombardment of the substrateimpregnated the substrate with carbon species, and thus, solvedpreviously encountered problems in getting the carbon film to nucleateon the substrate

The deposition conditions used with conventional and modified arc sourcefor carrying out the carbon films are summarized in Table C.

                  TABLE C                                                         ______________________________________                                        Summary of Graphite Arc Evaporation                                           Experimental Conditions                                                                     Modified      Conventional                                                    Arc Source    Arc Source                                                    Sample A Sample B  Sample C                                       ______________________________________                                        Substrate     HSS        Silicon   WC                                         Evaporation Current                                                                         50         50        50                                         Ic (A)                                                                        Substrate Voltage                                                                           -50        -50       -150                                       Us (V)                                                                        Magnetic Field                                                                              500        500       0                                          B (Gauss)                                                                     Gas Used      Ar         H.sub.2   None                                       Coating Pressure                                                                            25 mTorr   25 mTorr  10 -6 Torr                                 Film Thickness                                                                              2.5 um     1 uM      0.5 um                                     ______________________________________                                    

The hardness of the coatings was measured by using a Vickersmicrohardness tester. The adhesion strength of the films deposited onthe different substrates was tested with a VTT scratch tester. A Macbethcolorimeter was used to express the optical reflectance behavior of thedeposited carbon lawyers. The morphology of the carbon layers wasobserved by using a Scanning Electron Microscope and their surfaceroughnesses were quantified by a Dektak II A profilometer. The structureand the chemical bonding of the films were analyzed by Raman and FourierTransforms Infrared spectroscopy.

In order to define the effect involved in evaporating graphite cathodes,a first attempt was made to deposit carbon films using conventional arcprocess conditions, similar to those normally used with a titaniumcathode. The arc current intensity was set to 50 A and the substrate DCbias voltage during the coating phase was established to approximately-150 V for keeping constant the sample temperature at 150° C. No gassupport was used during the course of the 30 minutes experimental cycle.A substrate current of 2.5 A, as well as a voltage drop Uc across thedischarge space of 20 V, were measured.

As expected in view of previous efforts of this nature, the carbon arcdischarge exhibited a "monospot" at the cathode surface. Thisquasi-stationary spot moved very slowly along the edge of the cathode,with a velocity of less than 1 cm per second. Furthermore, the glowemitted from the discharge was very bright and the heat transfer to thesubstrate was significant. The plasma flux generated by carbon arcevaporation exhibited a high ionization degree reaching a maximum valueof 70 percent. This agreed with previously documented results, whichshow a correlation between the degree of ionization and the cathodematerial boiling temperature (which is 4500k for carbon material). Thoseskilled in the art will recognize that carbon demonstrates a negativeresistivity for temperature below 1000° K, which might explain the slowarc motion at the cathode surface and its tendency to preferentiallylocate where the carbon resistance is the lowest. This feature seems tolead to the observed arc instability and short discharge lifetime, whichrequire frequent re-triggering of the cathode. The above-mentionedeffect also tends to generate a large number of incandescent carbonparticles ejected simultaneously with the ionized plasma stream. As wasexpected, the HSS substrate held at a 150 mm distance from the carbonsource exhibited a powdery graphite coating having a very poor adhesion.SEM observation of the film surface, revealed substantial defects, whichare due to the unstable conditions of the conventional arc evaporation,leading to macroparticle ejections and low quality deposition.

When the magnetic field, induced by the magnet coil 51 of the plasmaenhancement apparatus 50, was activated, the random trajectory of thecathode arc spot was no longer displayed. The spot seems to be steeredto the surface center of the carbon cathode, where the lines of force ofthe magnetic field are substantially perpendicular to the cathode, andits axial component Bz is maximum. However, under a residual vacuumcondition of 10-6 mTorr, the arc discharge was still unstable and thecathodic spot was extinguished by the magnetic field when its valueexceeded several hundred Gauss. To sustain a very stable evaporation, agas support partial pressure of argon or hydrogen with a minimum valueof 5mTorr must be set during the process. The arc discharge obtained inthis stable condition displayed an arc column contraction and a brightgas glow discharge spot located in front of the cathode. These effectslead to an increase of the cathode temperature resulting in theimprovement of the discharge lifetime and the reduction of the observedemission of incandescent carbon macroparticles. Furthermore, when themagnetic field is applied, augmentation in the voltage drop Uc acrossthe discharge space to 40 Volts was measured for a 50 A arc currentintensity.

FIG. 7 shows the magnetic field influence induced by the magnet coil 51on the total ion current collected as the plasma exited the plasmaenhancement apparatus 50 as a function of the substrate bias voltageapplied. The saturation ion current measured by setting a 500 Gaussmagnetic field is much higher than that obtained with a conventional arcdischarge, when no external magnetic field is used. The saturationcurrent measured with a 80 mm diameter probe at the plasma exit point is5 A, corresponding to two times the total ion current collected withconventional arc discharge.

The curves presented in FIG. 8 demonstrate the influence of the magneticfield strength versus the saturation ion current collected by a -150 Vbiased probe, when the arc discharge is established at 25 mTorr partialpressure of argon or hydrogen gas. As illustrated in FIG. 8, theincrease of the magnetic field leads to a rise of the total saturationcurrent collected. Both measurements performed with argon or hydrogengas display saturation effect for a magnetic field value of around 500Gauss. The results illustrate the result of focusing the plasma with themagnetic field. The axial component Bz of the magnetic field with theazimuthal Hall current J flowing through the plasma, generate a radialforce Fr=J.Bz (Lorrentz force) focusing the plasma stream along theplasma guide. This effect results in magnetization of the electronsinvolving an increase of the electron-molecule and ion-moleculeinteraction probability and leading to further excitation and ionizationof the plasma flux species. An additional consequence of the magneticfield on the plasma stream is an increase in the average ion energy, asmeasured by a multi-electrode electrostatic probe in vacuum condition asa function of the magnetic field strength. This effect is the result ofradial component Br of the field which produces an acceleration forceFz=J.Br on the plasma stream leading to higher energy of the carbonions. These different experimental observations and results suggest thatthe enhanced arc apparatus improves the carbon arc discharge byincreasing the total ion flux collected by the substrate and controllingthe ion energy of the plasma stream.

The hardness of the carbon films deposited at a bias voltage of -50 V,on high speed steel (sample A) and silicon (sample B) substrates wasmeasured by using a diamond microhardness technique and applying loadingforces in the range of 10gf to 400gf. In this test the film thicknesswas measured as 2.5 um for sample A and 1 um for sample B. The indentdiagonal length was confirmed by SEM observation and the film hardnesseswere calculated using the relation HV=0.1891 F/d2, which had beenpreviously employed for determining the film hardness of a diamond-likecoating. Viewing the hardness of the different films as a function ofload increases from 10 gf to 400 gf, the hardness value discrepancymeasured for heaviest load, between film A and B, seems to be due to thethickness difference of the films and the substrate hardness inequality.The hardness of the film B deposited on silicon measured with a 400 gfexhibits a value of 1100 HV greater than silicon hardness value of 800HV. No hardness measurements for loads less than 25 gf were analyzedbecause the hard nature of the film leads to a too small indent size.However, average hardness of 2600 HV and 5200 HV with respectively 50 gfand 25 gf load have been measured for both samples A and B.

Using SEM surface topography analysis, the carbon films deposited by themodified arc process of this invention on high speed steel substratesare very smooth compared to conventional arc results. Fewermacroparticles (maximum diameter ≦500 A) and surface defects can beobserved, and measurements taken by a Dektak II A profilometer confirmthis observation, as both samples A and B had an Ra equal to 0.02 um.

Furthermore, SEM examination of the fracture cross section of the carbonfilm deposited on sample A exhibits a very dense and amorphous structurewithout columnar growth. The amorphous film uniformly follows thesubstrate surface and displays a very good adhesion level. No adhesivefailure was observed at the film substrate interface.

In order to check the adhesion level of the test films, the adhesionstrength was measured by scratch test method. For film A the acousticintensity increased until reaching the lower critical limit of adhesionat Lc=22N, while the adhesive failure of the coating at the interface isgiven for an upper critical load of 35N. For the Si substrate, thelowest value of the lower critical load was 15N, while a higher value ofthe upper critical load of 42N was measured in comparison to sample A.Furthermore, the film B exhibits a higher acoustical signal amplitudecompared to film A. The results from the scratch test correlated to SEMobservation of the scratch coating failures, showing that film A scratchmark exhibited more coating chipping than film B. Because of thedifferent natures of the substrates and the film thickness discrepancy,a comparative result is very difficult. Nevertheless, the critical loadsmeasured for the various substrate, and in particular high speed steel,were promising for carbon films on such materials.

To assess the nature of the carbon film deposited by enhanced arctechnique, the films obtained under hydrogen and argon partial pressurerespectively on silicon and high speed steel substrate were analyzed byRaman spectroscopy. Under a 25 mTorr partial pressure of hydrogen atroom temperature, the Raman spectra of a carbon filmed produced on asilicon substrate is quite typical of DLC films produced by ion beammethod. It presents only a diffuse peak at wave number of 1550 per cmand a very weak peak at 1350 per cm. The G peak at 1550 per cmcorresponded to the graphite crystal structure, while the D peak at 1350per cm was characteristic of defective graphite structure or crystallinestructure.

The Raman spectra of carbon films deposited onto high speed steelsubstrates under argon partial pressure conditions was quite odd. Themain peak, the G peak, was located at a wave number of 1560 per cm whilethe D peak centered at 1350 per cm always very broad in conventional DLCfilms was in this spectra weaker than previously observed under hydrogenconditions. The relatively high energy level exhibited by the G peaklead to an asymmetry of the spectra which is characteristic of amorphousnonhydrogenated DLC films. These results seem to indicate that thestructure of carbon films depends on ion energy involved during theirnucleation and growth and on the level of hydrogen contained in thefilm. Because the carbon film structure is influenced by the state ofthe carbon chemical bonding, analyses have been carried out by FourierTransforms Infrared Spectroscopy. As expected, the FTIR absorbancespectra of the film deposited on high speed steel substrates (Sample A)demonstrated the absence of C-H stretching absorption mode at the wavenumber of 3000 per cm which is a relatively reliable indicator that theDLC film deposited contains no hydrogen. This feature is different inthe FTIR spectra observed for the DLC film deposited on sample B underhydrogen partial pressure.

The deposited films under DC bias voltage with argon and hydrogenpartial pressure conditions exhibited a grey black color expressed byMacbeth color measurement as the following:

Sample A: L*=60.88 a*=0.37 b*=-1.55

Sample B: L*=55.90 a*=0.22 b*=-0.54

Also, reflectance curves showed that the optical reflectance did notexhibit a smooth curve, but instead oscillated between maximum andminimum, having an increasing amplitude as the wavelength increased.This phenomenon seems to result from the optically transparent nature ofthe arc deposited DLC films. The incident light beam is reflected byboth the air/film and film/substrate interfaces. The optical effectresulting leads to generate constructive and destructive interferences,indicated by the maximum and minimum reflectance measured. This phasedifference is dependent on the film thickness and the refractive indexof the film and also of the substrate. If the film were opticallyopaque, the incident light would not reach the film/substrate interfaceand thus no interference would occur. However, because the films areneither totally transparent or opaque, the degree ofconstructive/destructive interference will depend on the amount of lightabsorbed by the film. The experimental results indicate that the filmbecomes more absorbing at low wavelength when the amplitude betweenmaximum and minimum decreases. The films display a relative transparencyin the near visible infrared range with a maximum absorbance peak at660nm for film A and 560 nm for film B. However, the reflectance in the400-500 nm region being slightly higher indicates the bluish darkappearance of the film in ordinary light previously exhibited by the b*color value of the films.

The plasma enhancement apparatus magnetically confines the arc dischargeat the carbon cathode surface. The magnetic arc constraint leads to abetter spot stability and allows a longer discharge lifetime. Optimalevaporation conditions were achieved when the axial component of themagnetic field Bz was maximum at the center of the cathode surface. Themaximum magnitude of the axial field was obtained with lines of forceconfinement induced by optimal position of magnetic core piecesaccording to the embodiment shown in FIG. 3. The glow discharge spotproduced in the vicinity of the cathode surface indicates an increase ofexcitation and ionization of the plasma flux leaving the cathodesurface. This enhancement of electrons in this region is believed tocontribute significantly to the acceleration of the carbon ions. Thesecond important effect of the magnetic field occurs during the plasmastream transport, where a confinement of the plasma to a focused beam of20 mm in diameter can be observed. The ion losses by diffusion arereduced, and the plasma flux and the ion current density collected atthe plasma guide exit are considerably increased. An additionalconsequence of the focusing effect is the increase of the collisionalprocess during the plasma stream transport, which is believed to beresponsible for the reduction of the carbon macroparticles byevaporative phenomenon.

The plasma enhancement apparatus enhances the excitation and ionizationlevel of the plasma and accelerating the ions to higher energy. Also,the structure and the chemical bonding of the condensated films may becontrolled or affected by adjusting the condensation conditions, such asthe ion current density and the ion energy. With the carbon arcevaporation technique, the level of energy for DLC films nucleation andgrowth is gained from the kinetic energy of the ions impinging thesubstrate. Also, an ideal carbon ion energy for DLC deposition mustreportedly be in the range of several tens of electron volts, higherthan the binding energy of the carbon atoms and lower than the thresholdenergy leading to crystal defect (60 ev). In addition to the carbon ionflux, the experimental results indicate that the use of argon gasresults in argon ion bombardment of the film surface and sputtering ofthe graphitic constituent of the film.

The carbon ion energy is an important parameter because it affects thefilm evolution in different ways. It contributes to manage the adhesionand stress level of the film, to increase the sp³ hybridized carbon andconcentration of unprotonated quaternary carbon which appears to controlthe mechanical properties of the DLC films. It is understood that usingthe plasma enhancement apparatus of the present invention, the impingingcarbon ion energy is easily manageable by varying the bias voltageapplied to the substrate.

Additional Applications

Vapor deposition of titanium and carbon as described above constituteonly two examples of the utility and application of the presentinvention. Those skilled in the art will recognize various additionalapplications and modifications in view of the foregoing disclosure. Forexample, the core members need not be coaxial, nor even coplanarrelative to one another. In fact, certain applications may require thata series of core pieces be aligned relative to one another in such amanner to define a curved plasma stream. Additionally, one or more ofthe core members may be mechanically driven to "spray" a relativelynarrow plasma stream across a wide area. Such an application may bedesirable where a large object must be coated with a very high densitycoating.

Another attractive application involves the coating of inner surfaces oftubes and the like, where the penetration of the coating material intothe tube is a function of the diameter of the tube. The presentinvention makes it possible to generate and accelerate an intense narrowbeam of plasma, which will provide greater penetration into tubularstructures and the like. Such a narrow beam can be generated either byincreasing the thickness of the core piece or pieces nearest the exit ofthe plasma guide or by adjusting the aperture defined by the core pieceor pieces nearest the exit of the plasma guide. On the other hand, forapplications where it is desirable to distribute a fine coating over alarge area, as is the case with many mass production operations, thecore piece(s) nearest the end may be thinner.

For any given application, the core pieces comprising the core membercan be varied in size, shape, number, and position (relative to oneanother, as well as the magnet) until a suitable configuration isachieved. Such "fine tuning" capability is facilitated by the structureof the present invention. Accordingly, while the present invention hasbeen described with reference to two particular embodiments, variousalternative embodiments and design options will be apparent to thoseskilled in the art, and the present invention is to be limited only bythe appended claims.

What is claimed is:
 1. A plasma enhancement apparatus for use incombination with an electric arc vapor deposition system having a vacuumchamber, a consumable cathode source of coating material defining acathode evaporation surface and an anode operable with the vacuumchamber, means for supporting a substrate to be coated in spacedline-of-sight relation to said cathode, said line-of-sight extendingalong an axis line extending between said cathode evaporation surfaceand said substrate, means for initiating and sustaining an electric arcbetween the cathode evaporation surface and said anode to create acolumn of plasma material projecting in line-of-sight manner along saidaxis line in a vacuum space extending from said cathode evaporationsurface toward said substrate, comprising: field generating meansmounted relative to said cathode evaporation surface and said substrate,so as to maintain said line-of-sight therebetween, for generating amagnetic field having magnetic field lines arranged around said axisline and between said cathode evaporation surface and said substrate andof a configuration whereby said field lines are constricted in at leasta portion of said vacuum space; said magnetic field being furthercharacterized by having:a. strength and orientation relative to saidcathode evaporation surface that defines the intensity and confinedmovement of an arc spot of said arc over said cathode evaporationsurface so as to minimize the generation of macroparticles at saidcathode evaporation surface and to minimize their presence in saidcolumn of plasma material projected therefrom; and b. strength andorientation that energizes electrons of said column of plasma materialwithin at least a portion of said vacuum space, sufficiently to causemacroparticle vaporization therein, and that significantly increases theionization, ionic charge and ionization fraction of said column ofplasma material at said substrate; whereby highly ionized substantiallymacroparticle reduced coating material from said cathode source impingesupon said substrate.
 2. The plasma enhancement apparatus as recited inclaim 1, wherein that portion of said column of plasma materialimpinging upon said substrate is virtually macroparticle free and fullyionized.
 3. The plasma enhancement apparatus as recited in claim 2,wherein said cathode source comprises titanium.
 4. The plasmaenhancement apparatus as recited in claim 1, wherein said cathode sourcecomprises graphite material.
 5. The plasma enhancement apparatus asrecited in claim 4, wherein that portion of said column of plasmamaterial impinging upon said substrate is virtually free of hydrogen. 6.The plasma enhancement apparatus as recited in claim 1, wherein saidcathode source comprises difficult to a material with a high meltingpoint or vaporization temperature of the order of or greater than 2000°kelvin.
 7. The plasma enhancement apparatus as recited in claim 1,further including means for introducing a reactive gas into the vacuumchamber such that said reactive gas forms a portion of said column ofplasma material; and wherein said magnetic field enhances and improvesionization of said reactive gas adjacent said cathode evaporationsurface, thereby promoting formation of a compound layer on the cathodeevaporation surface, which further minimizes generation ofmacroparticles at said cathode evaporation surface.
 8. The plasmaenhancement apparatus as recited in claim 1, wherein said fieldgenerating means comprises in part, permanent magnets.
 9. The plasmaenhancement apparatus as recited in claim 1, wherein said magnetic fieldgenerating means comprises electromagnets.
 10. The plasma enhancementapparatus as recited in claim 9, including means for shaping said columnof plasma material about said axis line ; and wherein said fieldgenerating means are generally coaxially aligned with said axis line.11. The plasma enhancement apparatus as recited in claim 10, whereinsaid field generating means comprises an electromagnet with at least twocore members, forming a magnetic circuit; said core members defining agap within said magnetic circuit having an axial length, wherein saidmagnetic field extends across said gap and operatively engages and actsupon said column of plasma material along an axial focus zone coaxiallyaligned with said axis line, and having an axial length generallycorresponding to the axial length of said gap.
 12. The plasmaenhancement apparatus as recited in claim 11, wherein said fieldgenerating means comprises means for selectably changing said coremembers to selectably vary the axial length of said axial focus zone toaccommodate various deposition applications and the use of widelydiffering cathode source materials.
 13. The plasma enhancement apparatusas recited in claim 1, wherein said field generating means comprises anelectromagnet with at least two core members, forming a magneticcircuit; said core members defining a gap within said magnetic circuitwherein said magnetic field extends across said gap and operativelyengages and acts upon said column of plasma material.
 14. The plasmaenhancement apparatus as recited in claim 13, wherein said core memberscomprise selectable core piece means, that can be selectively changed,for varying the shape and magnitude of the magnetic field across saidgap.
 15. The plasma enhancement apparatus as recited in claim 1, whereinsaid field generating means comprises means for establishing a magneticcircuit having a plurality of distinct magnetic field segments withinsaid magnetic field and engaging said column of plasma material alongits longitudinal length, said plurality of distinct magnetic fieldsegments collectively defining a focus zone axially aligned along saidaxis line extending from said cathode evaporation surface to saidsubstrate.
 16. A process of enhancing electric arc vapor depositioncoating of a substrate within a vacuum deposition chamber by a plasma ofcoating material from a consumable cathode, comprising the steps of:a.operatively arranging an evaporation surface of a consumable cathodesource of coating material in line-of-sight position relative to asubstrate within a vapor deposition chamber; b. striking and maintainingan electric arc within said vapor deposition chamber, between saidcathode evaporation surface and an anode, to create a plasma of coatingmaterial from said cathode evaporation surface said electric arc formingone or more arc spots on said cathode evaporation surface; c. directinga column of said plasma in line-of-sight manner along an axis lineextending from said cathode evaporation surface toward said substrate;d. magnetically controlling the current density and movement of said arcspot over said cathode evaporation surface to reduce formation ofmacroparticles and to minimize their presence in said plasma column; e.magnetically energizing electrons in said line-of-sight plasma columnsufficiently to cause macroparticle vaporization therein and tosignificantly increase ionization, the ionic charge and the ionizationfraction of said plasma; and f. impinging said column of energizedplasma onto said substrate to form a smooth, dense and virtuallymacroparticle free coating on said substrate.
 17. The method as recitedin claim 16, wherein said cathode source of coating material comprisestitanium; and further comprising the step of cooperatively performingthe steps of magnetically controlling the current density and movementof the arc spot and of magnetically energizing electrons said plasmacolumn, so as to virtually completely ionize the plasma column materialthat impinges on the substrate.
 18. The method as recited in claim 17,further including the steps of: introducing a reactive gas into thedeposition chamber; and ionizing said reactive gas adjacent the cathodeevaporation surface to promote formation of a compound layer on thecathode evaporation surface that inhibits macroparticle emission intothe plasma column.
 19. The method as recited in claim 16, wherein saidcathode source of coating material comprises carbon-based material, andfurther comprising cooperatively performing the steps of magneticallycontrolling the current density and movement of the arc spot andmagnetically energizing said plasma column, so that a carbon streamvirtually free of hydrogen impinges on said substrate; thereby forming adiamond-like coating on said substrate.
 20. The method as recited inclaim 16 wherein the step of magnetically energizing the line-of-sightplasma column is performed in part by means of a magnetic circuit havingat least two core members; and further including the step of varyingselection of said core members to respectively accommodate variedcathode source materials.
 21. The method as recited in claim 20, whereinthe step of variably selecting said core members comprises selectivelyproviding a plurality of core members to define a magnetic circuithaving a magnetic field that intersects said plasma column along itsline-of-sight length, wherein the strength and shape of said field canbe accurately varied.
 22. A method of forming virtually macroparticlefree coatings on a substrate within an electric arc vapor depositionsystem which creates a plasma of coating material by striking anelectric arc between a consumable cathode and an anode within anevacuated deposition chamber, comprising the steps of:a. evacuating thedeposition chamber to a predetermined pressure; b. creating andmaintaining an electric arc between an evaporation surface of a cathodeand an anode, to produce a plasma of coating material projecting fromsaid evaporation surface; c. directing a column of said plasma ofcoating material in line-of-sight manner along an axis line between saidcathode evaporation surface and a substrate within said depositionchamber; d. magnetically controlling the intensity and movement of theelectric arc on the cathode evaporation surface so as to minimizegeneration of macroparticle emission into the column of plasma material;and e. applying a magnetic field to said column of plasma material, bypassing the column of plasma material through a core configuration whilemaintaining said line-of-sight manner of said column of plasma materialtoward the substrate, to increase the core energy of electrons of saidcolumn of plasma material sufficiently to vaporize macroparticles withinsaid column; whereby said column of plasma material arrives virtuallymacroparticle free at said substrate.
 23. The method as recited in claim22 further including the steps of:a. introducing a reactive gas into thedeposition chamber; and b. ionizing said reactive gas adjacent thecathode evaporation surface to promote formation of a compound layer atthe cathode evaporation surface to minimize generation of macroparticleemission into the column of plasma material.
 24. The method as recitedin claim 22, further including the step of applying a magnetic field tothe column of plasma material while maintaining its line-of-sightmovement to significantly increase the ionization, the ionic charge andthe ionization fraction of said column of plasma material prior toreaching said substrate.
 25. The method as recited in claim 24,including the step of coating a surface of the substrate with saidline-of-sight column of plasma material.
 26. The method as recited inclaim 25, further including the step of recovering from said depositionchamber the coated substrate having an adherent homogeneous, dense andvirtually macroparticle free coating.
 27. An enhanced electric arc vapordeposition system comprising:a. a vacuum deposition chamber; b. an anodeoperatively associated with said deposition chamber; c. a consumablecathode source mounted within said deposition chamber, said cathodesource defining an evaporation surface; d. a substrate; e. means forsupporting said substrate in spaced line of-sight relation to saidcathode evaporation surface within said vacuum deposition chamber; f.means operatively connected to said anode and said cathode source forestablishing and maintaining an electric arc between said cathodeevaporation surface and said anode, thereby creating a column of plasmamaterial projecting in line-of-sight manner along an axis line extendingfrom said cathode evaporation surface toward said substrate; and g.magnetic field generating means mounted so as to maintain theline-of-sight relation between said cathode evaporation surface and saidsubstrate, for creating a magnetic field having:i. strength andorientation relative to said cathode evaporation surface to control theintensity and movement of said arc over said cathode evaporation surfaceso as to minimize emission of macroparticles from said cathodeevaporation surface into said column of plasma material; and ii.strength and orientation relative to said column of plasma material toincrease the core energy of electrons of said column of plasma materialsufficiently to cause macroparticle vaporization therein, and tosignificantly increase the ionization, the ionic charge and theionization fraction of said column of plasma material at said substrate;whereby highly ionized reduced macroparticle plasma material from saidcathode impinges upon said substrate.
 28. The apparatus as recited inclaim 27, wherein said cathode comprises titanium.
 29. The apparatus asrecited in claim 27, wherein said cathode comprises carbon-basedmaterial.
 30. The apparatus as recited in claim 27, wherein said cathodecomprises a material with a high melting point or vaporizationtemperature of the order of or greater than 2000° kelvin, or whichdisplays negative temperature coefficient of resistivity.
 31. Theapparatus as recited in claim 27, wherein said magnetic field generatingmeans includes means for creating said magnetic field having strengthand orientation relative to said cathode evaporation surface sufficientto cause rapid confined movement of the arc across said cathodeevaporation surface and to split the arc into multiple cathode spots onthe cathode evaporation surface.
 32. The apparatus as recited in claim27, further including:a. means for introducing a reactive gas into thevacuum deposition chamber; and b. means for ionizing said reactive gasand for retaining large numbers of ions of said reactive gas directlyadjacent said cathode evaporation surface; thereby causing fewer andsmaller macroparticles to be emitted from said cathode evaporationsurface.
 33. The apparatus as recited in claim 27, wherein said magneticfield generating means creates said magnetic field having an orientationthat engages said column of plasma material along an axial focus zoneintermediate said cathode evaporation surface and said substrate, and astrength that increases the ionization fraction of the column of plasmamaterial leaving said axial focus zone to about 100 percent.
 34. Themethod of making a hard, smooth film coating directly on a substrate byelectric arc vapor deposition from a solid carbon source, said methodcomprising the steps of:a. forming a line-of-sight plasma within adeposition zone, under vacuum conditions, by means of an electric arcpassing between an arc spot on a consumable carbon-based cathode and ananode, said line-of-sight extending in the deposition zone between saidcathode and a substrate spaced therefrom; b. magnetically controllingthe arc at the cathode to increase the stability and lifetime of the arcspot on the cathode, thereby leading to reduction of macroparticleemission; c. magnetically converging the line-of-sight plasma by amagnetic field having strength and orientation for increasing the energyof electrons in said plasma core sufficient to atomize macroparticles;d. preparing a substrate within the deposition zone by impacting theline-of-sight plasma from step (c) onto a surface of the substrate tonucleate the substrate surface in preparation for coating; e. coatingthe nucleated substrate surface with said line-of-sight plasma from step(c); and f. recovering from the plasma deposition zone said substratehaving an adherent diamond-like carbon coating directly thereon, saidcoating being homogeneous, dense, smooth and extremely hard.
 35. Themethod of claim 34, wherein said plasma used in said coating step issubstantially free of macroparticles.
 36. The method of claim 34, inwhich the substrate is a metal substrate.
 37. The method of claim 34, inwhich the substrate is a ferrous metal.
 38. The method of claim 34,wherein the diamond-like coating has a thickness greater than about 3microns.